Glass ionomer cements are used by making a polymer acid primarily containing an acid such as a polycarboxylic acid and a glass powder for a glass ionomer cement react together to be cured in the presence of water. Glass ionomer cements have characteristics such that they are good in affinity to a living body, that they have superior adhesion to tooth substance such as enamel or dentin, and that they have tooth substance remineralization action and anti-caries action owing to fluorine contained in a glass powder. For these reasons, glass ionomer cements are materials widely used in dentistry for filling of a caries cavity, attachment of a crown, an inlay, a bridge or an orthodontic band, lining of a cavity, a sealer for filling a root canal, core construction, prophylactic sealing, and the like.
However, glass ionomer cements are low in mechanical strength such as compressive strength as compared with resin-based cements and the like including resin as a main component. When a stress is applied, the glass ionomer cements have a drawback that they are readily broken due to fine voids or defects in the interior of a cement cured product, cracks from scratches on a surface of the cured product, and the like. This is considered to be as follows: a matrix portion constituted by allowing a polycarboxylic acid, water, and a glass powder surface portion to react is brittle as compared with a glass portion constituted via a firm covalent bond of Si—O or Al—O and having a homogenous three-dimensional network structure, so that when a stress is concentrated into fine cracks generated in a part of the cured product, the cracks evade the glass portion having high strength and are rapidly expanded in the matrix portion having low strength, whereby the cured product is broken. As a result, in the dentistry, glass ionomer cements cannot be applied for filling a cavity to which a relatively large load is added, such as a class II cavity or a class IV cavity, and it has been reported that they are insufficient in mechanical strengths as compared with resin-based cements.
Along with a so-called “8020 campaign” (improvement in dental health, preservation of tooth substance (MI: Minimal Intervention)) to try to keep 20 or more own teeth even when being 80 years old, a remineralization therapy in which a site affected by caries is prevented from grinding as much as possible and a remaining site affected by caries is returned to the original with a material has recently got into the spotlight. A glass ionomer cement has been widely recognized also as a restorative material that slowly releases fluorine ions, which are known as an effective component for remineralization, and can possibly reduce the grinding amount of tooth substance. However, hydroxyapatite serving as a main constituent of tooth substance such as enamel or dentin is a compound comprising calcium or phosphorus, and efficient remineralization of a site affected by caries is not promoted sufficiently by supplying only fluorine ions to tooth substance.
Patent Document 1 discloses a glass ionomer cement powder containing apatite that fully makes use of biocompatibility and adhesion to tooth substance, both the biocompatibility and the adhesion to tooth substance being characteristics of a conventional glass ionomer cement, and is capable of increasing mechanical strength. It has been reported that mechanical strength, particularly three-points bending strength and tensile strength, increases as compared with the case where a conventional glass powder for a dental glass ionomer cement is used and that a glass ionomer cement can also be applied for filling a cavity to which a large load is to be added, the filling having been believed to be insufficient in conventional dentistry. Although the mechanical strength of a glass ionomer cement can increase, there is a problem that calcium or phosphorus, which is main constituents of tooth substance, cannot be supplied sufficiently to demineralized tooth substance, and efficient remineralization cannot be promoted by merely adding hydroxyapatite, which is believed to be most stable among calcium phosphates.
Non-Patent Document 1 discloses that when amalgam, a composite resin, and a glass ionomer cement having sustained fluorine releasability are filled into dentin cavities with remaining caries-like tissue, and then the degree of remineralization in each sample is evaluated after a lapse of 12 weeks with microradiography, and as a result, demineralization advanced in the caries-like tissues located near the cavities into which amalgam and the composite resin are filled, respectively, whereas remineralization is observed in the caries-like tissue near the cavity into which the glass ionomer cement is filled. Accordingly, it has been reported that a glass ionomer cement is an effective material for realizing preservation of tooth substance (MI: Minimal Intervention). As described above, however, a glass ionomer cement merely having sustained fluorine releasability cannot realize efficient remineralization, and a problem regarding low mechanical strength still remains unsolved.
As described in the prior art documents, the conventional technologies have a drawback that low mechanical strength and insufficient remineralization capability possessed by a glass ionomer cement cannot be solved, and solution of these problems have been desired.